DSB question

[Cal_stir]

I had a 6" sugarfine DSB in a lighted gium with cheato and it caked solid in @ 6 months, so I removed it and did an 8" sugarfine remote DSB in an unlit bucket and it did not cake in 6 months so I'm thinking it is something to do with the light or the algae, however, I eventually decided that they weren't worth the trouble and weren't controlling my nitrates and removed it.